Slag has many commercial uses, and is rarely discarded. It is often reprocessed to separate any other metals that it may contain. The remnants of this recovery can be used in railroad track ballast and as fertilizer. It has been used as a road base material and as a cheap and durable means of roughening sloping faces of seawalls to progressively arrest the movement of waves. Blocks of slag have been used in the construction of retaining walls and foundations.
What was once an unwanted by-product of the steel making process can now be recycled and used in the manufacture of high performance concretes. When iron ore is heated in a blast furnace the impurities or ‘slag’, which include large quantities of calcium and silica, become molten and are separated from the raw iron.
As the slag is channeled out of the furnace, thousands of gallons of water are poured over it. This rapid cooling, often from a temperature of around 2,600° C., is the start of the granulating process. This process causes several chemical reactions to take place within the material, and gives the slag its cementitious properties.
The water carries the slag in its slurry format to a large agitation tank from where it is pumped along a piping system into a number of gravel based filter beds. The filter beds then retain the slag granules while the water filters away and is returned to the system.
When the filtering process is complete, the remaining slag granules, which now give the appearance of coarse beach sand, can be scooped out of the filter bed and transferred to the grinding facility where they are ground into particles that are finer than portland cement
This previously unwanted recycled product is used in the manufacture of high performance concretes, especially those used in the construction of bridges and coastal features where its low permeability and greater resistance to chlorides and sulfates can help to reduce corrosive action and deterioration of the structure.
An interlocking paver is a pre-cast piece of concrete or brick commonly used as an alternative to plain concrete or asphalt or other paving materials. Pavers can be assembled to cover walkways, patios, pool decks and driveways and airport or loading docks. Interlocking pavers are available in a wide range of shapes such as rectangular, hexagonal, etc. and each allows them to be jointed fittingly to create a paving surface. The advantage of using interlocking pavers over the asphalt and poured concrete are high compressive strengths which can reach 7000+psi, pleasant look, time saving, easy removal and relaying etc.
There are quite a few traditional interlocking pavers available in the market. They are available in different shapes, sizes and made of different materials. Common building materials are concrete and clay, and by adapting different manufacturing methods pavers of various physical properties can be achieved. For example, pressing the dry concrete-mix into molds rather than pouring a wetter mix results in their 8000+psi compressive strength, making concrete paving stones a more durable choice than clay bricks or poured-in-place concrete. Clay pavers have an advantage with resistance to fading from the sun and deterioration from long term exposure to the elements. Because clay pavers are fired, the pores of the paver are at least partially vitrified closed, therefore creating an almost non-permeable surface. Another disadvantage of clay pavers is lack of choice of color spectrum. Clay pavers are formed from a natural material, so the feasible range of colors is more limited. Concrete, in contrast, has an essentially limitless color spectrum when starting with white portland cement and using pigments.
Installation of interlocking pavers starts with a compacted stone sub-base and a leveling bed of sand, pavers of desirable size, shape and material. Instead of connecting the pavers by pouring grout between the joints, as one would with tiles, sand particles are spread over the pavers and tamped down. The sand stabilizes the interlocking pavers yet allows for some flexibility. This type of pavement will absorb stress such as small earthquakes, freezes and thaws, and slight ground erosion by shifting each paver slightly. Therefore they are less likely to crack or buckle like poured cement.
Due to the increasing environment concerns, however, there has been a upward demand on permeable paving materials, which provide water permeable properties as well as strength for use as paving materials. Permeable paving materials allow moisture to filter through and replenish underground water tables and other water sources. It also helps to drain water into the ground and relieve stress on over taxed storm water systems during high rain conditions.
In the past, concrete pavers have contributed to the LEED (“Green Building”) rating system. Originally developed for the U.S. Department of Energy and standing for Leadership in Energy and Environmental Design, LEED is growing in use by design professionals in response to federal, state, and local government agencies, and by private developers. LEED uses a point rating system to recognize sustainable site and building design. Depending upon geographical location due to varying enabling legislation and practice in the different states, complying with the rating system is voluntary and it aims to improve environmental and economic performance of buildings and sites. Developed by consensus with the participation of many organizations, the rating system and certification program based on providing evidence of compliance to the rating system is administered by the U.S. Green Building Council. A complete description and downloads can be found on the Internet at www.usgbc.org/LEED.
Importantly, concrete pavers and permeable interlocking concrete pavers can earn points or “credits” in the LEED rating system. Credits are earned under several categories of use including stormwater management, local/regional materials, and exterior design to reduce heat islands. For stormwater management, Credit 6.1 (1 point) can be earned for building sites where the existing impervious area is greater than 50%. Permeable interlocking concrete pavement can meet this requirement. In some urbanized areas with this extent of impervious cover, permeable interlocking concrete pavement may be more cost-effective than separate water detention and/or retention facilities due to space and configuration constraints. The LEED requirement is that runoff rate and quantity be reduced by at least 25%. In the past, permeable interlocking concrete pavements have been able to reduce runoff to zero for the most frequent storms.
Credit 6.2 provides 1 point for treatment systems designed to remove 80% of the average annual post development total suspended solids (TSS), and 40% of the average annual post development total phosphorus (TP). The ability of permeable interlocking concrete pavements to reduce these pollutants is typically greater than these percentages according to references in the Interlocking Concrete Pavement Institute's manual, Permeable Interlocking Concrete Pavements—Selection, Design, Construction, Maintenance. The ICPI manual references studies on infiltration trenches (similar to permeable pavement bases) and porous pavements with reductions in TSS as high as 95% and TP as much as 70%.
Another source of credit is designated as Credit 5 (1 to 2 points), local regional materials: specify a minimum of 20% of building materials that are manufactured regionally within a radius of 800 km (500 miles). An additional point is earned if 50% of the regionally manufactured materials are extracted, harvested or recovered within this same radius. Most interlocking concrete pavers and permeable pavers will be manufactured within this distance from the project site.
Yet another Credit is 7.1 (1 point), landscape and exterior design to reduce heat islands. An option for meeting this requirement is to use light colored/high albedo materials with a reflectance of at least 0.3 for 30% of the sites non-roof impervious surfaces, i.e., pavements. Concrete paving units can be manufactured in practically any color, so they can be tailored to register an albedo of at least 0.3.
Albedo is defined as the ratio of outbound or reflected solar radiation to inbound radiation. It is measured with a pyranometer. A pyranometer is a type of actinometer used to measure broadband solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density in watts per square meter from a field of view of 180 degrees. The name pyranometer stems from Greek, “pyr” meaning “fire” and “ano” meaning “above” or “sky”. A typical pyranometer does not require auxiliary power to operate. Long-term measurements should be done with two pyranometers rather than one to better understand and compare diurnal changes in the radiation flux of pavements.
U.S. Pat. No. 6,419,740, issued Jul. 16, 2002 to Kinari et al. teaches a water-permeable solid material which can be used as paving materials. However, the materials are not and cannot be made into paver form. U.S. Pat. No. 6,824,605, issue Nov. 30, 2004 to De Buen-Unna, et al. also teaches ecological permeable concretes with high compression, bending and abrasion resistance for paving purposes, but again, the materials are not made into a paver form.
The American Concrete Institute defines a Supplementary Cementitious Material (SCM) as an “inorganic material such as fly ash, silica fume, metakaolin, or ground-granulated blast-furnace slag that reacts pozzolanically or hydraulically.” A material that reacts with by-products of the portland cement reaction to form additional binder material is a pozzolan. SCMs including fly ash and ground-granulated blast-furnace slag are often used to replace portland cement. Other SCMs, such as silica fume and other high silica content materials, are used to enhance various properties of concrete.
Processes for producing SCMs include mineralization via aqueous precipitation are known. FIG. 1A (Prior Art) shows one such process which utilizes carbon dioxide and other pollutants such as sulfur dioxide, fly ash, salt and other manufacturing process brines, waste water and sodium hydroxide to produce calcium carbonates, other green building materials and clean flue gas. Carbon dioxide from waste flue gas, such as that produced by typical energy plants which burn coal or other organic compounds, is converted into stable or metastable, solid calcium and magnesium carbonate and bicarbonate minerals, similar to those found in the skeletons of marine animals and plants. Typical mineralization via aqueous precipitation involves contacting flue gas from the power plant with natural waters found in abundance on Earth. Many of the crystallographic forms synthesized utilizing these processes make it possible to produce high reactive cements.
Unfortunately, prior uses of SCMs to replace portland cement in typical concrete have been unable to produce building materials having compressive strengths greater than 8000 psi using testing under ASTM C 1157 “Standard Performance Specification for Hydraulic Cement”. FIG. 1B (Prior Art) shows the results of testing done in accordance with ASTM C 109. This data shows that SCMs produce compressive strengths similar to portland cement at up to a 20% replacement of portland cement. These compressive strengths of between 2000 and 6000 psi are insufficient for use as paving stones in which compressive strengths of 8000+psi are required.
A carbon credit is a generic term for any tradable certificate or permit representing the right to emit one tonne of carbon or carbon dioxide equivalent (tCO2e). Carbon credits and carbon markets are a component of national and international attempts to mitigate the growth in concentrations of greenhouse gases (GHGs). One carbon credit is equal to one ton of carbon dioxide, or in some markets, carbon dioxide equivalent gases. Carbon trading is an application of an emissions trading approach. Greenhouse gas emissions are capped and then markets are used to allocate the emissions among the group of regulated sources. The goal is to allow market mechanisms to drive industrial and commercial processes in the direction of low emissions or less carbon intensive approaches than those used when there is no cost to emitting carbon dioxide and other GHGs into the atmosphere. Since GHG mitigation projects generate credits, this approach can be used to finance carbon reduction schemes between trading partners and around the world.
A carbon offset is a reduction in emissions of carbon dioxide or greenhouse gases made in order to compensate for or to offset an emission made elsewhere. Carbon offsets are measured in metric tons of carbon dioxide-equivalent (CO2e) and may represent six primary categories of greenhouse gases. One carbon offset represents the reduction of one metric ton of carbon dioxide or its equivalent in other greenhouse gases.
There are two markets for carbon offsets. In the larger, compliance market, companies, governments, or other entities buy carbon offsets in order to comply with caps on the total amount of carbon dioxide they are allowed to emit. This market exists in order to achieve compliance with obligations of Annex 1 Parties under the Kyoto Protocol, and of liable entities under the EU Emissions Trading Scheme. In 2006, about $5.5 billion of carbon offsets were purchased in the compliance market, representing about 1.6 billion metric tons of CO2e reductions. In the much smaller, voluntary market, individuals, companies, or governments purchase carbon offsets to mitigate their own greenhouse gas emissions from transportation, electricity use, and other sources. For example, an individual might purchase carbon offsets to compensate for the greenhouse gas emissions caused by personal air travel. Many companies offer carbon offsets as an up-sell during the sales process so that customers can mitigate the emissions related with their product or service purchase, such as offsetting emissions related to a vacation flight, car rental, hotel stay, consumer good, etc. In 2008, about $705 million of carbon offsets were purchased in the voluntary market, representing about 123.4 million metric tons of CO2e reductions. Offsets are typically achieved through financial support of projects that reduce the emission of greenhouse gases in the short- or long-term. The most common project type is renewable energy, such as wind farms, biomass energy, or hydroelectric dams. Others include energy efficiency projects, the destruction of industrial pollutants or agricultural byproducts, destruction of landfill methane, and forestry projects. Some of the most popular carbon offset projects from a corporate perspective are energy efficiency and wind turbine projects.